Chihaya and Taichi's train departs at Episode 5, 18 minutes 55 seconds. They still have a quarrel with Arata. "I shouldn't have come" Chihaya regrets. But she found Arata outside the window. Arata desperately chases Chihaya and Taichi's train on his bicycle.
From here to the bridge, is the same way Arata chased Chihaya and Taichi.